Method of magnetic core construction



Oct. 10, 1961 o. s. ATTEWELL unmon 0F MAGNETIC CORE cous'muc'rxon 2 shun-sum 1 Filed Nov. 13, 1956 INVENTOR. Olnsr G'flttauaZZ Oct. 10, 1961 o. G. ATTEWELL 3,003,226

ms'rnon OF MAGNETIC com: cousmucnou Filed Nov. 13, 1956 2 ShQOtS ShQOt 2 IN V EN TOR. Old ver 6 flttewell flttarny This invention relates to stationary induction apparatus and in particular to a method of constructing magnetic cores for stationary induction apparatus.

This application is a continuation-in-part of my ap- Uflitfid States Patent I or the method wherein right plication Serial No. 303,232 entitled Core for Electromagnetic Induction Apparatus," filed August 8, 1952, now U.S. Patent No. 2,942,218, and having the same assignee as the present invention.

Although wound magnetic cores of-continuous strip material having a preferred direction of grain orientation lengthwise thereof are ideal in that they provide minimum exciting current and minimum core loss, such continuous strip cores cannot be disassembled for-repair in the field in the event an electrical In order to permit disassembly of laminations of a wound core from a preformed. electrical winding it is well known to construct a magnetic core by cutting through a wound closed loopand'tojrcv'erse alternate turns to interleave the ends of the turns and provide two sets oi circumfcrentially spaced butt joints. My aforementioned application discloses that'cutting' a wound strip loop in a long a diagonal and reversing alternateturns in stacking to dispose the butt jointsformed by the diagonally cut ends opposite substantially uncut portions of adjacent laminations results in a core having remarkably low exciting current and core loss. However, the lamination: of

cores constructed by this methodofcutting through a single core and reversing alternateitnrns donot always intcrlit as tightly and compactly as desirable, and it may be necessary to apply mechanical force to hold the lamination ends in butt-jointed relation. This is particularly true when long diagonal cuts are made through the core and alternate turns are reversed so that the diagonalgbutt joints in adjacent layers cross. With this arrangement a lamination end cut at an obtuse angle meets a lamination end cut at an acute angle in each turn at'two corners 'ot the cone, andrelatively large. air gaps, as well as un desired openings where the joint: cross, may result unless means are provided to hold the lamination ends in buttjointed'rclation; i

" 1 itiis an'object of the invention to provide a novel method of constructing magnetic cores having lamina- Itions'which can be to and disassembled from a preformed-winding which substantially overcomes the aforementioned difiicui'ties inherentina method includ- 3,003,226 Patented Oct. 10, 1961 angle cuts are made thr ueh two similar loops andcertain turnsfrom each of the loops are reassembledto form a closed magnetic core;

FIGS.,6 and 7 illustrate another form of the method wherein cuts are made through both legs of each closed loop; and

FIGS. 8 and 9 illustrate still another form of the method of the invention wherein both wound loopsare cut at the same place. V e 1 g The present invention is a continuation-in-part of my .copending application Serial No. 303,232, new U.S. Patout No. 2,942,218, which discloses and claims a magnetic core having a long diagonal butt joint construction which provides considerably lower joint reluctance, core loss, and exciting current than prior'nrt cores having laminations which may be assembled to and disassembled from a preformed winding. The novel method of the present invention overcomes certain aforementioned shortcomings of the method and magnetic corewclaimcd in application Serial No. 303,232, and in accordance with the preferredembodiment oi the present invention illustrated in FIG. 1 two similar closed, convoluted, four-sided loops 10 and 1-1 are spirally wound from magnetic strip material having a direction of easiest magnetization lengthwise thereof. Preferably the magnetic ribbon for winding thetwo loops 10 and 11 is of approximately the same Width and is wound to approximately the same number of turns. Preferably the Winding is on a rectangular mandrel (not shown) to form the four-sided closedloops figuration prior to annealing. g

In accordance with the preferred embodiment of'the invention; cuts aremade through the loopsli) and 1-1 at ing the steps ofcuttin'g through a single wound core and reversing alternate turns? his aturther object or the invention to provide such an improved method of constructing magnetic cores whichresults in air gaps of minimum spacing between the cut'laminationends.

v r cinema-ens and advantagesof the invention be apparent thetoliowing' description when taken in conjtmction with the accompanying drawing wherein:

* 10. 1 is a view in perspective illustrating the steps ol'the methodofthelnvention wherein twosimilar closed loopsare wound and long diagonal cuts made through the loops at circumferentially spaced apart points; BIG. a is an exploded'perspective'view illustrating the a steps of concentrically stacking certain turns from eachoi the loops of FIG. '1' to construct a closed magct m e r t 'f FIG. 31is an exploded perspective view illustrating an alternative stacking of the turns;

FIGS. 4 and 5 illustrate steps of an alternative form circumi erentially spaced apart points 13 and 14. The

cuts may bemade by a saw or a thin abrasive cutting wheel rotating at high speed. As shown the cuts are made through what may be considered opposite .legs l5 and 16 of thetwo loops 10 and 11, but it will beap- I preciated that the method of the invention embraces the cutting of the two loops at circumfercntially spaced apart "points irrespective ofwhether one loop is cut in a wind- A ing. leg and the other loop is cut along a yoke or whether the cuts are made atcircumferentially spaced apart through'thesame side of bothloops. Inasmuch as the results of any previous annealing step are apt to beat least partially destroyed by cutting, the loops are preferably annealed after the cuts aremade at points 13' and .14, although the invention contemplates making the at 13 and 114subsequeirtto annealing.

As illustrated in FIGS. 1: and 2, each of the cuts at 13 and .14 isalong a diagonal having a length greater than \/2 times the width of the magnetic strip. 1- In the final core the butt joints between such diagonally cut lumination ends are disposed opposite substantially uncutisurfaces ofadjacent laminations. The reluctanceof 'a'butt joint is a .function of the amount oflmagnetic material in the portion of the adjacent layer opposite the joint. The magnetic flux density is equal in a layer having a butt joint and in a layer adjacent thereto; and with a right angle butt joint substantially all the magnetic .fiuxtrans- .fers to the portion of the adjacent layer opposite the joint and this portion saturates when the magnetic flux density in other portions of the core is only approximately fifty percent of saturation density. This crowding of flux inthe adjacent layer produces local saturation with the result that the reluctance of such a right angle butt joint is relatively high and there is a marked increase in exciting .current required to produce the total magnetic hux, the

value of which is fixed by the voltage of the apparatus. In the preferred embodiment the length of diagonal cuts at 13 and 14 is such that the portion of the adjacent lamination opposite the joint does not saturate prior to other portions of the core and consequently joint reluctance and exciting current are minimized. This improved result is attained in the preferred embodiment of the invention by making cuts through loops '10 and 11 having lengths greatthan x/i times the width of the magnetic strip material. If the butt joints are of a length twice the width of the magnetic strip, the amount of magnetic material 'in'a cross section through the adjoining layer along the line of the butt joint is equal to the area of magnetic material in a radial cross section through both the layer having the butt joint and the adjoining layer. My aforementioned application Serial No. 303,232, now 11.5. Patent No. 2,942,318, includes graphs illustrating the marked reduction in exciting current and core loss resulting from the increased length of butt joint and reference is made "thereto for details of the improved results.

'j" The loops 10 and 11 while held in quadrangular shape are subjected to a strain-relief anneal in an inert or other suitable gaseous atmosphere. The annealing step removes the deleterious strains introduced in the oriented magnetic material by the winding and cutting operations and perjmanently sets the turns in the shape they are held during annealing.

The turns formed by cutting the closed loops 10 and '11 at points 13 and 14 are then reassembled to form two closed magnetic cores in each of the which turns from loop '10 are adjacent turns from loop 11 and the butt joint between the respective ends of each turn-is opposite a substantially uncut portion of an adjacent turn. This cirfoumferential spacing of the butt joints in adjacent turns assures that the flux crossover at all the joints does not "occur in the same portion of the core and thus local saturation is avoided.

In accordance with the illustrated method of the instacked to construct a second magnetic core. The turns radially inward turn of loop 11. The turn 21 radially outward from turn 20 in the magnetic core is from loop 10 and comprises the second turn radially outward from the therein. The next radially outward turn 24 of the magnetic core is from loop 11 and comprises the third turn removed from the window therein. The fourth turn 25 radially outward from the. core window is from loop 10.

-In thismannerodd-numbered turnsfrom loop 1.1 and even-numbered turns from loop 10 are concentrically and 5, two substantially identical loops 10 and 11 are wound as described above, but right angle cuts are made at circumferentially spaced apart points 43 and 44 through the same yoke of both loops 10 and 11. One final core illustrated in FIG. 5 may be constructed by stacking odd-numbered turns 50, 52 etc. from one loop, e.g. loop 10, witheven-numbered turns 51, 53 etc. from the second loop 11; As illustrated in FIG. 4 a right angle I cut is made at 43 through the top yoke 45 of loop 10 at a vention certain turns from each of the loops 10 and 11 fare concentrically stacked to construct one magnetic core and the remaining laminations are concentrically window therein. The next radially outward turn 22 of the magnetic core is also from loop 10 and comprises the "third radially outward turn therein which is reversed 180 degrees before stacking. The fourth lamination 23 radially outward from the core window is from loop 11 and is reversed 180 degrees before stacking. This sequence of stacking to position turns from loop 11 adjacent turns from loop 10 is repeated until a first closed 'magnetic core is constructed, and the remaining turns from loop 10 and the remaining turns from loop 11 are concentrically stacked in a similar pattern to form a sec- 0nd magnetic core with turns from loop 10 adjacent turns from loop 11 and with the ends of each turn meeting end to end opposite an uncut portion of both adjacent turns. In the alternative form of the invention illustrated in FIG. 3 loops 10 and 11 are constructed as illustrated in 'FIG. 1, and odd-numbered laminations from loop 11 are concentrically stacked with even-numbered laminations from loop 16 to construct a first closed magnetic core, "and the remaining even-numbered turns from loop 11' are stacked with the remaining odd-numbered turns from loop '10to construct a second closed magnetic core.- Only one of the two magnetic cores constructed by this method of the invention is represented in the drawing, and as shown radially inward turn 20 of the magnetic core is the radially innermost turn of loop 11. Turn 21 radially outward 'from turn 20 of the magnetic core is from loop 10 and comprises the second turn removed from the window place to the left of the midpoint thereof, and a right angle cut is made at 44 through the top yoke 46 of core 11 at a place to the right of the midpoint thereof. After the two loops are annealed to preset the turns in desired quadrangular shape, a final core shown in FIG. 5 is constructed with the radially inward turn 50 thereof being the radially ,innermost turn of loop 10. The turn 51 of the magnetic 'core radially outward from turn 50 is the second turn bered turns from loop 10 are stacked with the remaining odd-numbered turns from loop 11 to construct a second magnetic core.

In the alternative method of the invention illustrated in FIGS..6 and 7, cuts are made through both winding legs of each of two identical wound loops 10 and 11 constructed in a manner described above. Long diagonal cuts are made at 63 and 65 through the winding legs of loop 10, and similar long diagonal cuts, but at angles complementary to cuts 63 and 65, are made at 64 and 66 through opposed legs of loop 11. A first magnetic core is then constructed by stacking odd-numbered turns 70,

72 etc. from one loop, e.g. loop 11, with even-numbered turns 71, 73 etc. from the second loop, e.g. loop 10. In

the first magnetic core the radially innermost turn 70 :comprising laminatons and 81 is from loop 11, and the next radially outward turn 71 comprising laminations 83 and 84 is from loop 10. The next outward turn 72 of the first magnetic core is from loop 11 and comprises laminations 85 and 86 having their diagonally cut ends in butt-jointed relation. The fourth turn 73 radially outward from the core window is from loop 10. This pattern of stacking is repeated until a first magnetic core is completed, and theremaining odd-numbered turns from loop 10 and the remaining even-numbered turns from loop 11 are stacked in a similar manner to construct a second magnetic core.

It will be appreciated that although the preferred embodiment of the invention has been illustrated and described as including the step of cutting loops 10 and 11 at circumferentially spaced apart points, it is within the spirit and scope of the invention to cut both loops 11 and 10 at the same place, e.g. at 89 as shown in FIG. 8,and to reassemble-odd-numbered turns 90, 92 etc. from one loop, e.g. loop 11, with even numbered turns 91, 93 etc.

Irons theother be, why rwersing the one lithe loops (as shown in 9 the turns 91, 93 cm. trees l op 10 are reversed) vto construct a first closed magnetic core wherein the ends of each turn meet end to end opposite a substantally uncut portion of an adjacent turn. In a similar manner a second closed magueticcore is'constructed by concentrically stacking the even-numbored turns from loop 11 with'the odd-numbered turns from loop 10 to position the butt joints opposite uncut portions of adjacent turns. It! cores constructed in accordance with the method of the inventon, it is unnecessary to force the lamination ends into butt-jointed relation The laminations inter-i ufit relatively compactly. the air gap spacing between lamination ends is a minimum, and norelatively wide openoccur where the. diagonal joints of adjscentlaminamoron as sometimes resultedin cores constructed in a accordance withthe method of my application Serial No. 303,232unleesmeans were provided to force the lamiinto butt-jointed relation.

Whileonly a few alternative methods in accordance with theinvention have been illustrated, and described, may modifications and'variations of the inven ion will be apparent to those skilled in the art, and it is intended in the appended claims to cover all such modifications and variations-as fall invention.

' l claim; l. The method of constructing magnetic cores for stainduction apparatus, comprising thesteps ofwindingmngneticstrip material fistwise to, form afoot-sided V dosedconvoluted structure, winding magnetic strip ma- ,tcrinl flntwise to ,form a second four-sided closed convolutedastructure substantially identical in size to said first structure, making a cut through one side of said first structure of alength greater than the fiatimes the Iiilhofthe magnetic strip makings cut through one side of said second structure at'a place differing from that at which said first structure iscut and of a length greater than the /2 times the width of said magnetic strip'material, whereby each structure includes a plurality of turns of progressively difierent peripheral length, disassembling the turns of both of said structures and reassembling in order of progressively different peripheral length given whole turns from said first structure and given whole turns from said second structure with the ends of each turn meeting end to end opposite a substantially uncut portion of an adjacent turn and with turns of said first structure adjacent turns of said second structure to form a first closed magnetic core, and reassembling in order of progressively difierent peripheral length the remaining whole turns from said first structure and the remaining whole turns from said second structure with the ends of each turn meeting end to end opposite a substantially uncut'portion of an adjacent turn and with turns of said first structure adjacent turns of said second structure to form a second closed magnetic core.

p 2. The method of constructing magnetic cores for stationary induction apparatus, comprising the steps of winding magnetic strip material flatwise to form a first foursided closed convoluted structure, winding magnetic strip material flatwiseto form a second four-sided closed convoluted structure substantially identical in size to said first structure, making a long diagonal cut through one side of said first structure of a length greater than the /2 times the width of saidmagnetic strip material, maka long diagonal cut through one side of said second structure of a length greater than the \/2 times the width of said magnetic strip material, the cuts being in the same side of both structures but extending in opposite directions, strain-relief annealing said first structure and said second structure to preset the turns thereof in four-sided configuration, disassembling the turns of both of said within the true spirit and scope of the fivenzwhole mm second structure with of saidfirst structure adjacent turns ofsaidsecond structure and with the diagonally cut ends of each turn meeting and to endto form a long di- 1 agonal butt joint and with the butt joints of adjacent turns crossing to form a first closed magnetic core, and concentrically stacking in order of progressively difierent peripheral length the remaining wholeturns of said first structure and the remaining whole turns of said second structure with turns of said first structure adjacent turns of said second structure and with the diagonally cutcuds of each turn meeting end to end and forming a long di agonal butt joint and with the butt joints of adjacent turns crossing each other to form a second closed magnetic core. i a

3. The method of constructing magnetic cores for stationary. inductance apparatus, comprising. the steps of winding magnetic strip material flatwise to foim a first four-sided closed convoluted structure, winding magnetic strip material flatwise'to forma second'four-sidcdcloscd peripheral length odd-numbered whole turns from said first structure and even-numbered whole turns from said second structure into n-closed magnetic core with the respective ends of each of said turns meetingiendto end opposite a substantiallyuncin portion of an adjacent turn, and concentrically stacking inorder of progressively dilierent peripheral length the even-numbered wholetnrns from said first structure and the odd-numbered whole .turnsot said second structure into a second closed magnetic core with the respective ends of each turn end to end opposite a substantially uncut portion of an adjacent turn. a

4. The method of constructing magnetic cores for stationary induction apparatus, comprisingthe steps of winding magnetic strip material flatwise toiform a first foursided closed convoluted structure, winding magnetic strip material fiatwise to form a second four-sided closed con voluted structure substantiallyidentical in size to said first structure, cutting through at least one side of said first structure, cutting through at least one side, of said second structure at a place differing from that at which said first structure is cut, disassembling the turns of both of said structures and reassembling in order of progressively different peripheral length given whole turns from saidfirst structure and given whole turns from said second structure into a first closed magnetic core with the turns ture and with theirespective cndsofeachturn'meeting s end to end opposite a substantially uncut portion of an adjacent turn, and reassembling in order of progressively different peripheral length the remaining whole turns from said first structure and the remaining whole turns from said second structure into a second closed magnetic core with the turns from said first structure adjacent turns from said second structure and with the ends of each turn meeting end to end opposite a substantially uncut portion of an adjacent turn.

5. The method of constructing magnetic cores for sta-' tionary inductance apparatus, comprising the steps of winding magnetic strip material fiatwise to form a first four-sided closed convoluted structure, winding magnetic strip material fiatwise to form a second four-sided convoluted structure substantially identicalin size to said first closed, structure,fcutting through one side of said first structure, cutting through one side of said second structure at a place diifering from that at which said first structure was cut, strain-relief annealing said first struc ture and said second structure to preset the turns thereof in four-sided configuration, disassembling the turns and concentrically stacking in order of progressively difi'erent peripheral length given whole turns from said first structure with given whole turns from said second structure so that the respective ends of each of said turns meet end to end opposite a substantially uncut surface of an adjacent turn and with turns from said first structure adjacent turns from said second structure to form a first closed magnetic core, and concentrically stacking in order of progressively different peripheral length the remaining Whole turns from said first structure with the remaining whole turns from said second structure so that the ends of each turn meet end to end opposite a substantially uncut portion of an adjacent turn and with the turns from "said first structure adjacent turns of said second structure to format second closed magnetic core.

i 6. The method of constructing magnetic cores for stationary induction apparatus, comprising the steps of 'winding magnetic strip material fiatwise to form a first I four-sided closed convoluted structure, winding magnetic strip material fiatwise to form: a second four-sided closed convoluted structure substantially identical in size to said "first structure, making a cut through one side of said first structure of a length greater than the /2 times the width of said magneticstrip material, making a cut through one side of said second structure of a length greater than the /2 times the width of said magnetic istrip material at a place differing from that at which said first structure is cut, disassembling the turns of both of said structures and concentrically stacking in orderof progressively different peripheral length odd-numbered whole turns from'said first structure and even-numbered whole turns .from said second structure into a closed magnetic core with the ends of each turn meeting end to end opposite the substantially uncut portion of an adjacent turn, and concentrically stacking in order of progressively difi'erent peripheral length the even-mun bered whole turns of said first structure and the oddnumbered whole turns of said second structure into a second closed magnetic core with the ends of each of said turns meeting end to end opposite a substantially uncut portion of an adjacent turn.

-7. In the method of constructing magnetic cores for stationary induction apparatus, the improvement comprising the steps of providing two substantially equal size, toursided, closed, convoluted annealed loops of flatwise wound magnetic strip having a permanent'set of foursided configuration, cutting through the convolutions of one of said loops to provide whole turn laminations each having a single joint therein and cutting through the convolutions of the second of said loops at a place circumterentially offset from the place of cutting of the first of said loops to provide whole turn laminations each having a single joint therein, and concentrically assembling odd-numbered whole turn laminationstrom said first loop with even-numbered whole turn laminations from said second loop into a closed magnetic core with the respective ends of each of said turns meeting end to end opposite a substantially uncutportion of an adjacent turn.

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